Ultrasonic diagnostic apparatuses are known as the specimen information acquisition apparatuses. Since the ultrasonic diagnostic apparatuses non-invasively make pictures indicating information in specimens to acquire the pictures, the ultrasonic diagnostic apparatuses are widely used in medical fields.
For example, ultrasonic tomographic images and ultrasonic Doppler images have heretofore been used in the ultrasonic diagnostic apparatuses. The ultrasonic tomographic images result from imaging of the inner structures of living bodies from reflection echo caused by the difference in reflectivity between tissues and the ultrasonic Doppler images result from imaging of blood flow speeds or the likes by using the Doppler effect of ultrasonic waves caused by blood flows.
In addition, the hardness of tissues measured by using ultrasonic waves is recently started to be used for tissue diagnosis. This is because the hardness of tissues is deeply related to pathological states. For example, it is known that sclerosis cancers including breast cancers and thyroid cancers are likely to be sclerotic, compared with normal tissues and benign tumors.
Furthermore, it is reported in recent years that cancers differ from benign tumors in their viscosity characteristics in mammary tumors. Viscoelastic characteristics including the viscosity characteristics are required to be evaluated, in addition to the measurement of the hardness of tissues, in the tissue diagnosis. Accordingly, in addition to the measurement of the distributions of the viscoelastic characteristics in living bodies by using the ultrasonic waves, pictures of the distributions of the viscoelastic characteristics in the living bodies and pictures of the structures of tissues in related art are required to be used in combination in the diagnosis of cancers of tissue regions and so on.
PTL 1 discloses an ultrasonic diagnostic apparatus that calculates the viscosity of a specimen. In the ultrasonic diagnostic apparatus in PTL 1, an ultrasonic probe including a pressure sensor provided on a surface of a transducer that transmits and receives ultrasonic waves is used to measure the strain distribution by using the ultrasonic waves and also measure the distribution of pressure to be applied on the specimen with the pressure sensor in order to calculate the values of the elasticity and the viscosity from the strain distribution and the pressure distribution. Since the distribution of the pressure that has been actually applied is measured, in addition to the measurement of the strain distribution, in the above configuration, it is possible to realize the distribution measurement with high accuracy without uniformly applying the pressure.
PTL 2 discloses an ultrasonic diagnostic apparatus as a pressure measurement method. In the ultrasonic diagnostic apparatus in PTL 2, a deformation part for measurement the modulus of elasticity of which is known is sandwiched between an ultrasonic probe and a body tissue to measure the pressure. Specifically, the deformation in the deformation part for measurement is measured by using the ultrasonic waves and the pressure (stress) applied on the deformation part for measurement is calculated from the relationship between the modulus of elasticity and the strain to calculate the distribution of the modulus of elasticity in the specimen from the stress and the strain distribution in the specimen and display the calculated distribution of the modulus of elasticity.
However, the structure of the ultrasonic probe is complicated in the configuration described in PTL 1. In addition, there is a problem in that, when the strain distribution of tissues is measured by using the ultrasonic waves, it is difficult to measure the strain distribution of tissues with a normal pressure sensor because the pressure (stress) to be applied is normally very small. Furthermore, there is a problem in that, when the pressure sensor is provided immediately below the ultrasonic probe, it is not possible to perform the measurement for deep regions because the efficiency and the sensitivity of transmission and reception of the ultrasonic waves are degraded.
The ultrasonic diagnostic apparatus in PTL 2 is simple in the configuration. However, only the elasticity distribution in a specimen is displayed and a method of measuring the viscosity distribution in the specimen is not disclosed in PTL 2. Accordingly, there is a need for an apparatus capable of calculating the viscosity of a specimen with a simple configuration.